1. Field of the Invention
The present invention relates to a magnetic head assembly with electrostatic discharge (ESD) shunt/pads seed layer and, more particularly, to a highly conductive multi-layer seed layer on a slider which serves as a seed layer for exposed electrical pads on the slider and can be patterned to provide a shunt between read pads thereof.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm urges the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic field signals from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a spin valve sensor for sensing the magnetic signal fields from the rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer structure and a ferromagnetic free layer structure. An antiferromagnetic pinning layer interfaces the pinned layer structure for pinning a magnetic moment of the pinned layer structure 90xc2x0 to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the magnetic disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough.
In addition to the spin valve sensor the read head includes nonmagnetic electrically nonconductive first and second read gap layers and ferromagnetic first and second shield layers. The spin valve sensor is located between the first and second read gap layers and the first and second read gap layers are located between the first and second shield layers. In the construction of the read head the first shield layer is formed first followed by formation of the first read gap layer, the spin valve sensor, the second read gap layer and the second shield layer.
First and second leads are connected to the read sensor and extend therefrom between the first and second read gap layers and beyond the gap layers inside the slider to first and second lead ends which are located at an exterior surface of the slider. Third and fourth leads are connected across the write head and extend within the slider to spaced apart third and fourth lead ends at the exterior surface of the slider. First, second, third and fourth electrical pads are connected to the first, second, third and fourth lead ends for further connection to additional leads which connect the read and write heads to the aforementioned processing circuitry. During construction and assembly of the slider and the read and write heads, the sensor of the read head must be protected from electrostatic discharge (ESD) since the read sensor is a very small conductive element. The risk of damage to the write coil due to ESD is much less since it is a much larger conductive element. A discharge with only a few volts between the spaced apart first and second read pads can destroy or severely damage the read sensor. Such a discharge can occur by contact with or close proximity to a person, plastic involved in fabrication or components of the magnetic disk drive.
A typical arrangement for protecting the read sensor from ESD is to interconnect the first and second read pads with a thin film conductive line (shunt) on the exterior surface of the slider. This shorts the read circuit, preventing a discharge there across. The best time during assembly to form the conductive shunt between the pads is at the wafer level.
Magnetic heads are typically formed in rows and columns on the wafer which may be aluminum oxide/titanium carbide (Al2O3/TiC). At the wafer level the conductive shunts are formed between the read pads for shorting the read sensors. After formation of the magnetic heads the wafer is cut into rows. Each row is then cut into individual heads with a portion of the wafer serving as a slider for supporting the magnetic heads. Each slider with the heads mounted thereon is mounted on a head gimbal assembly (HGA) which, in turn, is mounted on a suspension which, in turn, is mounted on an actuator arm. A plurality of actuator arms may then be mounted in an actuator assembly to form a head stack assembly (HSA). From the time of forming the conductive shunts up to the time of forming the HSA the read sensors are protected from ESD. The next step is to merge the HSA with a disk stack assembly to form a complete disk drive which step is referred to in the art as xe2x80x9cmergexe2x80x9d. The most practical time to sever the conductive shunt of each read head so that the read head becomes operational is just before merge. This severing is typically done by a laser beam.
The slider material has very low electrical conductivity and therefore cannot function as a seed layer for plating the pads of the conductive shunt (if plated). A conductive seed layer, typically sputtered, is employed for plating the pads and to act as the whole or part of the conductive shunt. The slider typically has an overcoat of aluminum oxide (Al2O3) at the location of the pads and the conductive shunt. Gold (Au) is a desirable material for the conductive shunt but has very poor adhesion to the aluminum oxide overcoat. Also, adhesion between patterning resist and gold is poor.
The present invention provides a multi-layer seed layer on the exterior surface of the slider which can be employed for making the aforementioned pads and, after making the pads, can be patterned to form a conductive shunt between the first and second read pads. The conductive shunt has an electrically conductive adhesion layer which interfaces the surface of the slider and an electrically conductive layer, which is preferably gold (Au), with the adhesion layer being located between the slider and the conductive layer. A preferred adhesion layer is tantalum (Ta) or chromium (Cr). The conductive shunt preferably includes a cap layer with the conductive layer being located between the adhesion layer and the cap layer. The cap layer is preferably nickel iron chromium (NiFeCr) or rhodium (Rh).
An object of the present invention is to provide a magnetic head assembly with a seed layer on the surface of a slider which can be used for electroplating read and write pads followed by patterning of the seed layer to form a conductive shunt between first and second read pads.
Another object is to provide the seed layer of the previous object with multi-layers to provide good adhesion to the slider as well as providing high electrical conductivity and, after protecting the read head from ESD, can be easily severed with a laser.
A further object is to provide a method of making the foregoing read heads.